Oxidation resistant alloy



United States Patent 3,031,297 OXIDATION RESISTANT ALLOY Sanford Baranow, Mason, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Filed Nov. 3, 1959, Ser. No. 850,730 3 Claims. (Cl. 75126) This invention relates to high temperature, oxidation resistant alloys and, more particularly, to alloys of iron, chromium, calcium and yttrium.

For applications in air, the held of high temperature metallurgy is, for most practical purposes, limited to the utilization of oxidation resistant iron base and nickel base alloys, and the use of even these materials is limited to temperatures not in excess of 2000 F. The only other generally available materials which might be expected to have useful strength, oxidation resistance above 2000 F. and workability are chromium base or iron-chromium base alloys. While high temperature, high strength, structural, chromium base and iron-chromium base alloys do exist, the usefulness of such alloys has been limited by oxide film formation on the surface of such alloys which does not afiord suflicient protection against further oxidation at high temperatures. The chromium oxide film which is formed during heating of the metal in air provides some useful protection at temperatures up to 2000 F. Above this temperature, oxidation is sufiiciently rapid to discourage use of the metal at such elevated temperatures.

In copending application, Serial No. 842,517 filed September 25, 1959, in the names of James A. McGurty and John F. Collins, a ternary oxidation resistant iron-chromium alloy is disclosed and claimed which consists of from 0.5 to 5.0 weight percent yttrium, from 20.0 to 95.0 weight percent chromium, and the balance being iron. Iron-chromium base alloys with small amounts of yttrium are stable in air to temperatures well above 2000 F. These ternary alloys of iron, chromium and yttrium have good oxidation resistance at temperatures in excess of 2000 F.

Iron-chromium base alloys which would provide high strength, good oxidation resistance and cladding protection for base alloys at temperatures in excess of 2000 F. are desirable. The invention of the present application provides such iron-chromium base alloys with improved workability and an improved oxide film.

It is an object of my invention to provide an alloy of iron, chromium, calcium and yttrium.

It is another object of my invention to provide an iron-chromium base alloy with an improved oxide film.

'It is another object of my invention to provide an iron-chromium base alloy with improved workability.

It is a further object of my invention to provide an alloy which has superior oxidation resistance at temperatures in excess of 2000 F.

In carrying out my invention in one form, from 0.005 to 0.015 weight percent calcium, and from 0.5 to 1.5 weight percent yttrium are combined with an iron-chromium base alloy having from 20.0 to 35.0 weight percent chromium and the balance of iron to provide a high temperature, oxidation resistant alloy with improved workability and an improved oxide These and various other objects, features and advan- "ice tages of the invention will be better understood from the following description.

I discovered unexpectedly that small additions of calcium and yttrium to iron-chromium base alloys produced alloys which had superior oxidation resistance in air at temperatures in excess of 2000 F., improved workability, and improved oxide films. The addition of from 0.005 to 0.015 Weight percent of calcium, and from 0.5 to 1.5 weigh percent yttrium to iron-chromium alloys having from 20.0 to 35.0 weight percent chromium and the balance of iron provided these extraordinary eflects. While this weight percent of calcium improved this alloy, 0.01 weight percent calcium appeared to be the optimum amount of this addition to the alloy.

During the research which led to the discovery of these oxidation resistant iron-chromium alloys, a series of small vacuum melted iron-chromium-calcium-yttrium buttons were prepared. These alloy buttons, containing from 0.005 to 0.015 weight percent calcium, from 0.5 to 1.5 weight percent yttrium, from 20.0 to 35.0 weight percent chromium and the balance of iron, were heated in air at 2300 F. for hours. The specimens were then examined metallographically and weight changes measured. The data tabulated in Table I shows the excellent stability of the iron-chromium base alloys containing calcium and yttrium as compared with iron-chromium base alloys.

While other modifications of this invention which may be employed within the scope of the invention have not been described, the invention is intended to include all such as may be embraced within the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An alloy of iron, chromium, calcium and yttrium which consists of from 0.005 to 0.015 weight percent calcium, from 0.5 to 1.5 weight percent yttrium, from 20.0 to 35.0 weight percent chromium, and the balance being iron.

2. An alloy of iron, chromium, calcium and yttrium which consists of 0.01 weight percent calcium, from 0.5 to 1.5 Weight percent yttrium, from 20.0 to 35.0 weight percent chromium, and the balance being iron.

3. An alloy of iron, chromium, calcium and yttrium which consists of 0.01 weight percent calcium, 1.0 weight percent yttrium, 25.0 weight percent chromium, and the balance being iron.

FOREIGN PATENTS Great Britain July 12, 1938 

1. AN ALLOY OF IRON, CHROMIUM, CALCIUM AND YTTRIUM WHICH CONSISTS OF FROM 0.005 TO 0.0015 WEIGHT PERCENT CALCIUM, FROM 0.5 TO 1.5 WEIGHT PERCENT YTTRIUM, FROM 20.0 TO 35.0 WEIGHT PERCENT CHROMIUM, AND THE BALANCE BEING IRON. 